Water-asbiology edexcel

Water notes

all you need to know :)

And good luck in your exams

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  • Created by: sophie
  • Created on: 13-03-12 18:59


  •  Water is a polar molecule with no overall charge.
  • The 1 oxygen molecule is slightly negative
  • While the 2 hydrogen molecules are slightly positive
  • Thus held with HYDROGEN BONDS which make it liquid at room temp.
  • The O end is attracted to negative molecules and vice versa with hydrogen
  • Solvent-polarity means they attract other polar molecules, and chemical reactions can take place. – for example it makes a good TRANSPORT MEDIUM in blood.
  • (This is called intermolecular bonding)
  • Water itself can be involved in reactions such as condensation and hydrolysis reactions, which you should learn too.) :)
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Thermal Info.

  • The reason that water turns to ice at 0°C is that as the water is cooling the molecule doesn’t have enough energy to break the hydrogen bonds as it requires a lot
  •  The water becomes locked in a crystalline lattice as the hydrogen bonds make the molecules more spaced out.
  • Water cools and warms slowly because it takes a HUGE amount of energy to increase by a SMALL amount of degrees
  • This is useful to organisms to help them keep a steady temperature even if the temperature in their surroundings is varying
  • It also helps enzymes to catalyse
  • When water freezes, the ice is less dense than the water. This insulates what is beneath it which is why whole oceans, lakes etc. don’t completely freeze all the way to the bed
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Cohesion and Adhesion

  • Cohesion: the intermolecular forces  water molecules
  •  Adhesion: intermolecular forces between cellulose and water
  • This helps water ascend through xylem in plant stems.
  • And keep remembering its all about hydrogen bonding
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Hydrophobic and Hydrophilic

  •  Just in case you find this hard to remember, hydroPHOBIC; when you have a phobia its because you are afraid of something, HYDROphobic; hydro is like water, so substances such as lipids are ‘afraid of water’ and don’t dissolve.
  • Lipids- for them to be transported in the blood they combine with proteins to form LIPOPROTEINS.
  • Hydrophilic- ‘water loving’ polar molecules dissolve easier in water. E.g. sugars and amino acids. If you remember what hydrophobic means then you should find it easy to remember that hydroPHYLIC is just the opposite.
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